The present invention relates to methods of stabilizing bactericidally active acid divalent silver (Ag(II)) complexes into solid matrices. Said complexes constitute the subject matter of U.S. Pat. No. 5,017,295 of the present inventor. In said patent, the inventor described the preparation of soluble Ag(II) complexes which are effective bactericides in water utilized for industrial cooling and for swimming pools. Of the various complexes described, the most viable ones were the Ag(II) phosphates. These are prepared by dissolving divalent silver oxide (AgO) in phosphoric acid. It was demonstrated by the inventor in numerous experiments that those conditions which favored the formation of divalent silver ions were most effective bactericides, so that there exists a definite correlation between bactericidal activity and favorable Ag(II) stability in solution. Two conditions that favor Ag(II) ion stability are low pH and the addition of oxidation agents.
These favorable conditions have been described in the chemical literature. The stabilization under acid conditions of Ag(II) ions can be expressed by the following equation: EQU AgO.sup.+ AG.sup.+ +2H.sup.+ =2Ag.sup.2+ +H.sub.2 O
Said Ag(II) phosphate complexes are stabilized in concentrated phosphoric acid solution. The handling of said solutions poses a safety hazard to the user who is advised in Material Safety Data Sheets accompanying the product to use gloves and goggles when handling the solution. Furthermore, the shipping of such material requires hazardous labeling as a corrosive substance. Accordingly, it was desired to develop a solid form that could stabilize the Ag(II) acid complexes. After experimenting with a series of solid absorbents, it was found that anhydrous calcium sulfate when mixed in the proper ratio with various Ag(II) acid complexes would stabilize and set into hard plaster-like compositions containing the complexes. These hard compositions could be ground into solid powders giving rise to a viable product. Furthermore, the fact that calcium sulfate performed in this manner added another feature to the product, and that was it could be added directly to swimming pools where calcium chloride is employed as a mineralizing agent, and thus there would be no necessity to add calcium chloride in addition to this sanitizer to the pool.